1. Field of the Invention
The present invention relates in general to a pixel structure and a method for forming the same, and more particularly, to a pixel structure having a storage capacitor.
2. Description of the Related Art
Referring to FIG. 1, a cross-sectional view of a conventional pixel structure is shown. The pixel structure 100 has a substrate 109 which has a semiconductor layer 120 formed thereon. The semiconductor layer 120 and the substrate 109 are covered by an insulating layer 150. The insulating layer 150 has a gate electrode 116 formed thereon and covered by an interlayer dielectric layer 190. The insulating layer 150 and the interlayer dielectric layer 190 have two openings 162 for exposing the semiconductor layer 120. A source electrode 114, a drain electrode 112 and a capacitance electrode 101 are formed on the interlayer dielectric layer 190. The source electrode 114 and the drain electrode 112 are electrically connected to the semiconductor layer 120 through the opening 162.
A passivation layer 102 formed on the interlayer dielectric layer 190 covers the source electrode 114, the drain electrode 112, and the capacitance electrode 101, and the passivation layer 102 has a contact hole 163 for exposing the source electrode 114. The pixel electrode 103 is formed on the passivation layer 102 and is electrically connected to the source electrode 114 through the contact hole 163.
The capacitance electrode 101 of the pixel structure 100 is made of a conductive material, and the passivation layer 102 is made of a dielectric material. The storage capacitor Cs1 is formed between the capacitance electrode 101 and the pixel electrode 103. However, due to the covering method of the passivation layer 102, the pixel electrode 103 and the capacitance electrode 101 are easily short-circuited during the manufacturing process. Despite the above problem can be resolved by increasing the thickness of the passivation layer 102, the storage capacitor Cs1 is decreased relatively.
Besides, the capacitance electrode 101 is made of a non-transparent material and is located within a visible area (not illustrated in the diagram) of the pixel structure 100. Despite the pixel electrode 103 is made of a transparent material, such design enables the aperture ratio of the pixel structure 100 to decrease because of the increase in the storage capacity of the storage capacitor Cs1 (such as the area of the storage capacitor Cs1 within the visible area), resulting in a decrease in the brightness of a panel. Such problem arises more often in a panel of the same size but with higher resolution.